Sodium petroleum sulfonates are widely used as the primary emulsifier in formulating emulsifiable lubricating compositions used for cutting fluid, hydraulic fluids, metalworking lubricants, and so forth.
Sodium petroleum sulfonates are typically produced as a by-product of refining processes in which certain highly refined petroleum products such as white lubricating oils, medicinal oils, and certain grades of transformer oils, are produced. The highly refined petroleum products are produced by treating a refined petroleum distillate or raffinate with fuming sulfuric acid which reacts with certain components of the oil to produce sulfonic acids, some of which are oil-soluble and some of which are water-soluble, thus forming a two-phase system. The two phases separate into two layers one of which is the oil layer containing the oil-soluble reddish-brown or mahogany sulfonic acids, and one of which is the water-soluble layer commonly referred to as an acid sludge layer that contains resinous materials, unreacted sulfuric acid, and water-soluble or green sulfonic acids. The layers are then separated and the oil-soluble sulfonic acids are recovered from the oil layer, usually in the form of their sodium salts.
The mahogany sulfonic acids being preferentially oil-soluble have found wide use in the preparation of emulsifiable petroleum products, such as in soluble cutting oils, hydraulic fluids, metalworking lubricating fluids for forming of metals, and so forth. The acid oil layer is neutralized to make a sodium salt and extracted with a polar solvent, typically alcohol, to separate most of the oil phase, and to increase the activity of the sodium sulfonate. This type of process is discussed generally in U.S. Pat. No. 1,930,488. The manufacture of white oils by the above process has become increasingly uneconomical and as a result, the production of sulfonates as by-products of white oil refining is substantially declining. This has left a significant shortage of sodium petroleum sulfonates.
Another major disadvantage with the natural petroleum sulfonates is their inconsistency in quality, and hence a variance in their emulsifying properties. In order to improve emulsification properties, secondary surface active agents of different types are often added, for instance, fatty acid salts. The amount of the secondary surface active agent used is varied depending on the quality of the sulfonate being employed. U.S. Pat. No. 4,140,642 describes an improved emulsifier composition in which salts of alkylaryl sulfonic acids are employed with an organic or mineral base, and in which the equivalent weights of the acids are distributed according to a function of C=f(M) where C denotes the concentration and M denotes the equivalent weight of individual acids, which function has two distinct equivalent weight maximum M.sub.1 and M.sub.2, with M.sub.1 &lt;M.sub.2. Surprisingly, the present inventors have found a blend of sulfonates that provides an emulsifier composition that has consistent emulsification properties, and that is economical as well. This blend comprises at least one natural alkali metal petroleum sulfonate that is not prepared as a by-product of an oil refining process and may be non-extracted, and a blend of other high active synthetic sulfonates or sulfonic acids selected so as to produce an emulsification system that has 60% or greater active content, and selected so as to balance the oil solubility and emulsification performance thus providing an excellent surfactant system.